A passenger jet taking off from Gatwick was involved in a near miss with another aircraft after one nearly caught up with the other when climbing.

Air Traffic Control at the London airport “forcefully instructed” the aircraft behind to cease its ascent and take a harsh right turn so that it did not get any closer to the plane ahead.

The incident in April this year involving two Airbus 319s, which can carry 156 passengers each, was investigated by the UK Airprox Board (UKAB), who concluded that the cause of the mishap was the air traffic controller’s failure to scan his radar before clearing the second pilot to climb.

“He should have seen [the first aircraft] ahead,” an official report said. It was then that he “issued avoiding action”.

Another contributing factor was that the usual gap of two minutes between planes taking off was reduced to 45 seconds, which is a “regular situation”. Poor coordination by air traffic control was also found to be a factor.

The report said: “The [two] pilots shared an equal responsibility for collision avoidance and not to operate in such proximity to other aircraft as to create a collision hazard. Notwithstanding… it is the responsibility of the controllers concerned to ensure that standard separation requirements are met.”

UKAB found that the planes came within 700 feet vertically and 2.2 miles horizontally, less than the 1,000 feet vertically and 3.5 miles required, and concluded that “safety had been degraded”.

The board also expressed disappointment that the pilot of the first aircraft, operating a “foreign-registered aircraft”, had not filed a report.

It assessed the incident and rated it as category C, the third most serious.

How close is too close?

"During cruise, planes will always be a minimum of 1,000 feet apart vertically or three miles horizontally," according to Patrick Smith, pilot and author of Cockpit Confidential. "With simultaneous approaches to parallel runways planes can be at the same altitude and a mile or less apart - though they remain under the very close watch of ATC and must also maintain visual contact with one another."